1. Field of the Invention
This invention relates to an electrophotographic apparatus and particularly, to an electrophotographic apparatus having an image-holding member of improved durability and cleaning property for holding electrostatic images and/or toner images.
2. Description of the Prior Art
An electrostatic image or toner image is formed by various electrophotographic processes. As the image-holding member on which an electrostatic image or toner image is formed, there are an electrophotographic photosensitive member and other image-holding members.
The electrophotographic photosensitive members as variously constituted are prepared according to the predetermined characteristics of the members and electrophotographic process to be applied thereto. As typical photosensitive members, there are members having a photoconductive layer formed on a support and members provided with an insulating layer on the surface of the former member. These members are used in wide fields. The photosensitive member consisting of a support and photoconductive layer is employed in the image formation based on the most general electrophotographic process which comprises charging, image exposing and developing steps, and further a transferring step if desired. As for the photosensitive member provided with an insulating layer, such layer is formed for the purpose of protecting the photoconductive layer, improving the mechanical strength of the photosensitive member, enhancing the dark decay characteristic of the member, or adapting the member to the specified electrophotographic process. Typical photosensitive members having such an insulating layer or examples of the electrophotographic process using the member having an insulating layer are disclosed, for example in U.S. Pat. No. 2,860,048, Japanese Patent Publication No. 16429/1966, and U.S. Pat. Nos. 3,146,145; 3,607,258; 3,666,363; 3,734,609; 3,457,070; and 3,124,456.
To the electrophotographic photosensitive member, the predetermined electrophotographic process is applied so that an electrostatic image is formed, and then the image is visualized by development.
Process for using and forming some of the typical image-holding members other than the electrophotographic photosensitive member will be given below:
(1) Image-holding member used in the electrophotographic process which comprises forming an electrostatic image on a photosensitive member, transferring the image to the image-holding member for the purpose of improving the repeating usability of the photosensitive member, developing the transferred image and transferring the toner image to a recording material. This process is disclosed, for example in Japanese Patent Publication Nos. 7115/1957, 8204/1957 and 1559/1968.
(2) Image-holding member used in the electrophotographic process which comprises forming an electrostatic image on an electrophotographic photosensitive member in a screen form having a large number of fine openings by the predetermined electrophotographic process, applying corona charging treatment to the image-holding member through the electrostatic image to modulate the ion flow from the corona so that the electrostatic image is formed on the above image-holding member, developing such image with a toner, and transferring the toner image to a recording material thereby forming the final image. This process is disclosed, for example in Japanese Patent Publication Nos. 30320/1970 and 5063/1973, and Japanese Patent Laid Open No. 341/1976 as the electrophotographic process in which an electrostatic image corresponding to that formed on the photosensitive member is formed on the image-holding member.
(3) Image-holding member employed in the electrophotographic process which comprises forming a toner image on an electrophotographic photosensitive member, transferring the toner image to the image-holding member without directly transferring it to a recording material, and transferring the toner image from the image-holding member to a recording material followed by fixation. This process is effective, particularly for forming a color image and copying at a high speed. Most of the recording materials are usually flexible, such as for example paper and film. As a result, in case of transferring cyan, magenta and yellow images directly onto such a recording material, it is difficult to register the positions of the images. On the contrary, if the cyan, magenta and yellow images are transferred onto the image-holding member which can be formed from a barely deformable material with the positions of the images registered and the transferred image is further transferred onto the recording material, a color image in which the positions of the images are more exactly registered can be obtained on the recording member. In addition, it is also effective for high speed copying such that a toner image is transferred to a recording material through the image-holding member.
(4) Image-holding member employed in the electrophotographic process which comprises applying electric signal to the multi-stylus electrode to form an electrostatic image corresponding to the electric signal on the image-holding member and developing the image. The image-holding members (1)-(4) do not require a photoconductive layer.
As mentioned above, not only the electrophotographic photosensitive member, but also various members having an insulating property at the surface are employed as the image-holding member on which an electrostatic image or toner image is formed. Usually, the surface of the image-holding member is reused many times. Upon reuse, new toner image is repeatedly formed on the surface of the image-holding member each time the process for forming the toner image is repeated. Therefore, it is necessary to remove totally the toner remaining on the surface of the image-holding member and to clean such surface when the process cycle for the image formation is completed, that is, after the toner image is transferred. As the method of removing the remaining toner, there are: the method of wiping and scraping the toner off the surface of the image-holding member by a cleaning blade, the method of wiping off the toner by a web like material to rub the surface of the member, the method of wiping off the toner by a fur brush and the like, and other methods. However, when the toner remaining on the surface of the image-holding member is removed by those methods, the cleaning efficiency of the methods is lowered in most cases as the frequency of using repeatedly the image-holding member is increased, and as a result, even if the surface of the image-holding member is cleaned by the methods, a portion of the toner remains on the surface.
The cause of this phenomenon is that the lubricating property of the surface of the image-holding member is lowered and therefore, separation of the toner becomes difficult.
Cleaning according to the above-mentioned method is conducted by a mechanical dynamic contact between the surface of the image-holding member and the cleaning means. Therefore, once the toner, remaining on the surface of the member at the time of cleaning the surface, agglomerates or fuses resulting in adhering to the surface of the image-holding member, then a ghost image or stripe appears on the formed toner image, or the surface of the image-holding member is damaged. Further, in case of an image-holding member such as a photosensitive member, the photoconductive layer is peeled off and in case of an image-holding member such as a member composed of a photoconductive layer and an insulating layer overlying the photoconductive layer, the insulating layer is peeled.
Further, when corona discharging is repeated as the charging treatment for forming an electrostatic image on the image-holding member and the member is exposed to the corona discharging for a long time, the electric characteristics in the surface of the member are deteriorated due to the formation of corona ion. This phenomenon is caused by the fact that ionized oxygen, nitrogen, carbonic acid gas, water, ammonia and the like are generated by the energy at the time when the corona ion collides directly with the surface of the image-holding member or by the corona discharging. They adhere to the surface of the member so that the molecule of the material constituting the surface is broken or oxidized and the surface of the member is deteriorated, or the above mentioned ionized substance adsorbs moisture. As a result, the surface electric resistance of the image-holding member is lowered, and therefore such member cannot retain the electrostatic charge so that the member cannot be used as the desired image-holding member.
For the purpose of reusing the image-holding member to which the remaining toner adheres or whose electric characteristic is deteriorated, it is necessary to recover the initial surface state of the member by abrading the surface to expose a new surface.
For such recovery of the initital surface characteristics, a conventional technique such as described in Japanese Patent Laid Open No. 47346/1973 employs a developer containing both abrasive and lubricating agent so as to maintain lubricating property of the surface of the image-holding member and abrade the surface of the image-holding member to expose a new surface. However, it is difficult to keep the ratio of the abrasive to the lubricating agent constant and physical properties of the developer are deteriorated.